The disclosure relates to generally to polycarbonates and methods for producing the polycarbonates, and more particularly, to polycarbonate copolymers, methods for producing the polycarbonate copolymers, and articles thereof.
Polycarbonate homopolymers are widely used in a variety of applications by virtue of their excellent physical properties, such as impact resistance, mechanical characteristics, transparency, and the like. Bisphenol A (BPA) polycarbonate, the industry benchmark material, by virtue of its low cost, good transparency, and mechanical properties, has served as the substrate of choice for optical data storage media, such as, for example, compact disks and digital versatile disks (DVD). However, the need to store greater amounts of information on individual disks has resulted in newer techniques for high-density data storage based on multiple information layers and shorter wavelength lasers. Exemplary high-density storage disks include high density DVD (HDDVD), digital video recordable (DVR), DVD-recordable (DVDxe2x88x92R and DVD+R), and DVD-rewritable (DVDxe2x88x92RW and DVD+RW) formats. The high-density storage disks include a transparent plastic layer that forms a non-interfering shielding layer. The transparent plastic layer preferably exhibits high transparency, heat resistance, low water absorption, and ductility, specifications that standard BPA homopolycarbonates fail to meet.
One property that influences the efficacy of a given material for higher data storage density is the spacing between the pits and grooves on the substrate material. Since data is stored in these pits and grooves, the flatness of the disk is necessary to prevent loss of information. It is known that excessive moisture absorption by the disk can result in skewing (also referred to as warpage) of the disk or the films that form the disk, which in turn leads to reduced reliability for reading and writing data. This skewing, hereinafter referred to as dimensional stability, will result in data being stored or read inaccurately by the laser beam. Since the bulk of the disk is generally comprised of polymer material, the flatness of the disk depends on the low water absorption of the polymeric material. For example, a film produced from conventional BPA polycarbonate often exhibits warpage due to absorption of ambient moisture. The dimensional stability is a function of, among other factors, the amount of ambient moisture present as well as the rate of moisture absorption. In addition to possessing dimensional stability, a satisfactory material for such advanced format optical disks should also be capable of replication and cycle time vis-à-vis the conditions employed for manufacturing conventional optical disks, such as compact disks. In order to produce disks suitable for high-density storage through injection molding, the polymer should also be easily processible, that is, exhibit good flow. Therefore, there is a continued need for developing new materials suitable for use in advanced data storage formats that provide effective dimensional stability, replication and cycle times, without compromising on any of the other desirable characteristics that BPA homopolycarbonate already possesses.
Disclosed herein is a polycarbonate copolymer comprising structural units derived from: a cyclohexylidene bis(alkylphenol) compound represented by a formula comprising: 
wherein A1 is a trisubstituted aromatic radical having the formula C6H3R2, wherein R2 is selected from the group consisting of C1-C6 alkyl radicals, and combinations comprising at least one of the foregoing radicals; an alkyl-substituted bisphenol represented by a formula comprising: 
wherein A2 is a substituted or unsubstituted aromatic radical; and R1 is selected from the group consisting of C13-C22 alkyl radicals; and a carbonic acid diester compound.
A melt transesterification polymerization method for producing a polycarbonate comprises combining a catalyst and a reactant composition to form a reaction mixture; and mixing the reaction mixture under reactive conditions for a time period to produce a polycarbonate product, wherein the reactant composition comprises: a carbonic acid diester of the formula (ZO)2Cxe2x95x900, where each Z is independently an unsubstituted or substituted alkyl radical, or an unsubstituted or substituted aryl radical; a cyclohexylidene bis(alkylphenol) of the formula: 
wherein A1 is a trisubstituted aromatic radical having the formula C6H3R2, wherein R2 is selected from the group consisting of C1-C6 alkyl radicals, and combinations comprising at least one of the foregoing radicals; and an alkyl-substituted bisphenol of the formula: 
wherein A2 is a substituted or unsubstituted aromatic radical; and R1 is selected from the group consisting of C13-C22 alkyl radicals;
In another embodiment of the disclosure, a melt transesterification polymerization method for producing a polycarbonate copolymer comprises combining a catalyst comprising at least one of sodium hydroxide or tetramethylammonium hydroxide, and a reactant composition to form a reaction mixture; and mixing the reaction mixture under reactive conditions for a time period to produce a polycarbonate product, wherein the reactant composition comprises: diphenyl carbonate, a cyclohexylidene bis(alkylphenol) of the formula: 
a long chain alkyl-substituted bisphenol of the formula: 
wherein R1 independently comprises a C13-C22 long chain alkyl radical; and at least one aromatic dihydroxy compound comonomer selected from the group consisting of resorcinol, bisphenol A,4,4xe2x80x2-(1 -decylidene)-bisphenol, 2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane, and mixtures thereof.
The above-described embodiments and other features will become better understood from the detailed description that follows.